Temporal niche partitioning: Mechanism of coexistence or competitive exclusion via priority effects?

Research Highlight: Ekrem R., de Vries, C., Kaiser, T., & Kokko, H. (2025). Temporal niche differentiation often leads to priority effects rather than coexistence: Lessons from a marine midge. Journal of Animal Ecology, https://doi.org/10.1111/1365-2656.70094. Temporal niche partitioning has always been hypothesized as a key mechanism in maintaining species coexistence. By utilizing resources or habitats at different times, each species will occupy distinct 'temporal niches', thereby reducing overlap in resource use and the potential for competitive exclusion. However, to what extent temporal niche partitioning can explain coexistence remains contested, as increasing theoretical and experimental evidence finds weak contributions of such temporal mechanisms to community dynamics. In a recent study, Ekrem et al. (2025) shed new light on this debate by studying the complex life history of coexisting strains of the marine midge, Clunio marinus. Using mathematical models based on empirical processes, they found that the temporal differentiation of breeding phenology between strains does not always lead to coexistence. Instead, the first strain that emerges and breeds will benefit from a positive frequency dependence, leading to priority effects that promote the exclusion of other strains. These results highlight the nuanced role of temporal niche partitioning and related mechanisms in contributing to coexistence, emphasizing the importance of system-specific knowledge in considering the consequences of temporal differentiations in resource and habitat use.